1. Field of the Invention
The present invention relates to a control system for an internal combustion engine, and particularly to a control system which performs a fuel injection control for injecting fuel into a combustion chamber of the internal combustion engine, wherein a pilot injection is performed before a main injection.
2. Description of the Related Art
Japanese Patent Laid-open No. 2005-48739 (JP '739) discloses a control system for a diesel engine, which performs a fuel injection that includes a combination of a pilot injection and a main injection. According to the control system disclosed by JP '739, when an output torque of the engine needs to be reduced when the gears of an automatic transmission are shifted, a fuel injection amount is reduced. In such a case, when a fuel injection amount of the main injection is increased, an execution timing of the main injection is retarded, and when a fuel injection amount of the pilot injection is reduced, an execution timing of the pilot injection is advanced.
The control method disclosed in JP '739 aims to suppress a change in the air-fuel ratio when performing the output torque reduction control of the engine. However, a combustion noise is not taken into consideration when performing the disclosed control method. Therefore, if the control method disclosed in JP '739 is executed or otherwise performed, a problem wherein combustion noises increase due to combustion of the fuel injected by the pilot injection, occurs. A reason why the combustion noises increase is believed to be that the intake air flow rate temporarily becomes excessive with respect to an amount of the injected fuel when performing the reduction control of the output torque, and the combustion of the fuel injected by the pilot injection proceeds rapidly.